This invention relates to a thermal storage unit which can recover, store and take out as desired heat energy including natural energy such as solar energy, terrestrial heat, etc., and artificial energy such as waste heat industrially generated, etc., thereby utilizing effectively said energy.
Energy storage systems may be broadly classified into the sensible heat system in which solar heat, etc. is given to a thermal storage material such as water, sand, etc. to be stored therein and the temperature itself possessed by them is taken out to be utilized, the latent heat system in which melting heat or gasifying heat, etc. accompanied with phase change is utilized and the chemical reaction heat system in which thermal storage is effected by allowing a thermal storage material to undergo a endothermic-exothermic reaction to convert the energy into chemical energy.
Among these energy storage systems, the thermal storage unit employing the latent heat system is higher in storage density and efficiency as compared with the thermal storage units of other systems, and also excellent economically with respect to a simple system, and further excellent in having also in combination the advantage of enabling enhancement of running efficiency of auxiliary equipment, because output and input of heat can be done at a constant temperature, and therefore has been utilized and investigated in various fields such as solar house, solar system for uses in industry, heat generating system and further cosmic heat generation.
Such latent thermal storage unit generally includes the capsule type 9 as shown in FIG. 8, comprising a plurality of capsules 11 arranged within a vessel 10 having an introducing inlet 10a and a discharging outlet 10b for heat medium (fluid) and a thermal storage material 4 filled within said capsule 11, and the shell-tube type 12 as shown in FIG. 9 comprising heat transfer tubes 14 through which fluid passes between the thermal storage materials 4.
Fluid progresses through the introducing inlet and is brought into contact with the thermal storage material through the capsules, etc.
However, according to either heat exchange methods of the capsule type and the shell-tube type, there is involved the problem that the heat exchange capacity is remarkably lowered by heat resistance of the solid phase attached on the heat transfer surface during heat release.
As a means for solving this problem, there has been proposed the method in which heat exchange is effected with good efficiency by direct contact with the heat medium instead of through capsules or heat transfer tubes. This effects direct contact with ethylene glycol as a heat medium by stabilizing the shape of high density polyethylene as a thermal storage material without flowing or sticking to each other even when melted, but it is difficult to stabilize the shape, and also there is the problem that this method is hardly applicable to thermal storage materials for high temperature.
Also, most of organic polymeric substances and inorganic compounds to be used generally for thermal storage materials have large volume changes accompanied with phase change between solid phase and liquid phase. Accordingly, there is also involved the problem that deformation may occur in the vessel such as capsules, etc. holding the thermal storage material, or that cracks may occur in the solid phase, thereby lowering heat exchange capacity.
To cope with such problem, as shown in FIG. 10 and FIG. 11, there has been proposed a device with the thermal storage material being housed in small sections to be scattered with little influence from volume change by providing a plurality of projections 16 or providing partitioning portions 18, etc. as a thermal storage material housing chamber outside of a heat transfer tube 15 or 17, respectively.
However, in this case, the heat transfer tube 15 or 17 and the thermal storage material housing chambers 16 or 18 provided therearound are required to be made of complicated structures, whereby the preparation steps become also complicated to a remarkable economical disadvantage. Further, enlargement of the contact area between the fluid and the thermal storage material is limited, and thus it has been desired to develop a thermal storage unit which can effect further improvement of heat exchange capacity.
Further, in cosmos under minute gravitational force, when employing the capsule type and the shell-tube type of the prior art, the latent thermal storage material becomes apart from the heat transfer surface during melting, whereby there is also a fear that the heat exchange capacity may be extremely lowered. Also, for the thermal storage unit for use in cosmos, weight reduction thereof has been particularly desired.